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April 21, 2020

Convergent horizontal gene transfer and cross-talk of mobile nucleic acids in parasitic plants.

Horizontal gene transfer (HGT), the movement and genomic integration of DNA across species boundaries, is commonly associated with bacteria and other microorganisms, but functional HGT (fHGT) is increasingly being recognized in heterotrophic parasitic plants that obtain their nutrients and water from their host plants through direct haustorial feeding. Here, in the holoparasitic stem parasite Cuscuta, we identify 108?transcribed and probably functional HGT events in Cuscuta campestris and related species, plus 42?additional regions with host-derived transposon, pseudogene and non-coding sequences. Surprisingly, 18?Cuscuta fHGTs were acquired from the same gene families by independent HGT events in Orobanchaceae parasites, and the majority are highly expressed in the haustorial feeding structures in both lineages. Convergent retention and expression of HGT sequences suggests an adaptive role for specific additional genes in parasite biology. Between 16 and 20 of the transcribed HGT events are inferred as ancestral in Cuscuta based on transcriptome sequences from species across the phylogenetic range of the genus, implicating fHGT in the successful radiation of Cuscuta parasites. Genome sequencing of C. campestris supports transfer of genomic DNA-rather than retroprocessed RNA-as the mechanism of fHGT. Many of the C. campestris genes horizontally acquired are also frequent sources of 24-nucleotide small RNAs that are typically associated with RNA-directed DNA methylation. One HGT encoding a leucine-rich repeat protein kinase overlaps with a microRNA that has been shown to regulate host gene expression, suggesting that HGT-derived parasite small RNAs may function in the parasite-host interaction. This study enriches our understanding of HGT by describing a parasite-host system with unprecedented gene exchange that points to convergent evolution of HGT events and the functional importance of horizontally transferred coding and non-coding sequences.

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April 21, 2020

Chromosome-level hybrid de novo genome assemblies as an attainable option for non-model organisms

The emergence of third generation sequencing (3GS; long-reads) is making closer the goal of chromosome-size fragments in de novo genome assemblies. This allows the exploration of new and broader questions on genome evolution for a number of non-model organisms. However, long-read technologies result in higher sequencing error rates and therefore impose an elevated cost of sufficient coverage to achieve high enough quality. In this context, hybrid assemblies, combining short-reads and long-reads provide an alternative efficient and cost-effective approach to generate de novo, chromosome-level genome assemblies. The array of available software programs for hybrid genome assembly, sequence correction and manipulation is constantly being expanded and improved. This makes it difficult for non-experts to find efficient, fast and tractable computational solutions for genome assembly, especially in the case of non-model organisms lacking a reference genome or one from a closely related species. In this study, we review and test the most recent pipelines for hybrid assemblies, comparing the model organism Drosophila melanogaster to a non-model cactophilic Drosophila, D. mojavensis. We show that it is possible to achieve excellent contiguity on this non-model organism using the DBG2OLC pipeline.

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April 21, 2020

Plasmid-encoded tet(X) genes that confer high-level tigecycline resistance in Escherichia coli.

Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant Gram-negative and Gram-positive bacteria1. Tigecycline resistance has sporadically occurred in recent years, primarily due to chromosome-encoding mechanisms, such as overexpression of efflux pumps and ribosome protection2,3. Here, we report the emergence of the plasmid-mediated mobile tigecycline resistance mechanism Tet(X4) in Escherichia coli isolates from China, which is capable of degrading all tetracyclines, including tigecycline and the US FDA newly approved eravacycline. The tet(X4)-harbouring IncQ1 plasmid is highly transferable, and can be successfully mobilized and stabilized in recipient clinical and laboratory strains of Enterobacteriaceae bacteria. It is noteworthy that tet(X4)-positive E.?coli strains, including isolates co-harbouring mcr-1, have been widely detected in pigs, chickens, soil and dust samples in China. In vivo murine models demonstrated that the presence of Tet(X4) led to tigecycline treatment failure. Consequently, the emergence of plasmid-mediated Tet(X4) challenges the clinical efficacy of the entire family of tetracycline antibiotics. Importantly, our study raises concern that the plasmid-mediated tigecycline resistance may further spread into various ecological niches and into clinical high-risk pathogens. Collective efforts are in urgent need to preserve the potency of these essential antibiotics.

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April 21, 2020

Antibiotic susceptibility of plant-derived lactic acid bacteria conferring health benefits to human.

Lactic acid bacteria (LAB) confer health benefits to human when administered orally. We have recently isolated several species of LAB strains from plant sources, such as fruits, vegetables, flowers, and medicinal plants. Since antibiotics used to treat bacterial infection diseases induce the emergence of drug-resistant bacteria in intestinal microflora, it is important to evaluate the susceptibility of LAB strains to antibiotics to ensure the safety and security of processed foods. The aim of the present study is to determine the minimum inhibitory concentration (MIC) of antibiotics against several plant-derived LAB strains. When aminoglycoside antibiotics, such as streptomycin (SM), kanamycin (KM), and gentamicin (GM), were evaluated using LAB susceptibility test medium (LSM), the MIC was higher than when using Mueller-Hinton (MH) medium. Etest, which is an antibiotic susceptibility assay method consisting of a predefined gradient of antibiotic concentrations on a plastic strip, is used to determine the MIC of antibiotics world-wide. In the present study, we demonstrated that Etest was particularly valuable while testing LAB strains. We also show that the low susceptibility of the plant-derived LAB strains against each antibiotic tested is due to intrinsic resistance and not acquired resistance. This finding is based on the whole-genome sequence information reflecting the horizontal spread of the drug-resistance genes in the LAB strains.

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April 21, 2020

RNA sequencing: the teenage years.

Over the past decade, RNA sequencing (RNA-seq) has become an indispensable tool for transcriptome-wide analysis of differential gene expression and differential splicing of mRNAs. However, as next-generation sequencing technologies have developed, so too has RNA-seq. Now, RNA-seq methods are available for studying many different aspects of RNA biology, including single-cell gene expression, translation (the translatome) and RNA structure (the structurome). Exciting new applications are being explored, such as spatial transcriptomics (spatialomics). Together with new long-read and direct RNA-seq technologies and better computational tools for data analysis, innovations in RNA-seq are contributing to a fuller understanding of RNA biology, from questions such as when and where transcription occurs to the folding and intermolecular interactions that govern RNA function.

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April 21, 2020

The persimmon genome reveals clues to the evolution of a lineage-specific sex determination system in plants

Most angiosperms bear hermaphroditic flowers, but a few species have evolved outcrossing strategies, such as dioecy, the presence of separate male and female individuals. We previously investigated the mechanisms underlying dioecy in diploid persimmon (D. lotus) and found that male flowers are specified by repression of the autosomal gene MeGI by its paralog, the Y-encoded pseudo-gene OGI. This mechanism is thought to be lineage-specific, but its evolutionary path remains unknown. Here, we developed a full draft of the diploid persimmon genome (D. lotus), which revealed a lineage-specific genome-wide paleoduplication event. Together with a subsequent persimmon-specific duplication(s), these events resulted in the presence of three paralogs, MeGI, OGI and newly identified Sister of MeGI (SiMeGI), from the single original gene. Evolutionary analysis suggested that MeGI underwent adaptive evolution after the paleoduplication event. Transformation of tobacco plants with MeGI and SiMeGI revealed that MeGI specifically acquired a new function as a repressor of male organ development, while SiMeGI presumably maintained the original function. Later, local duplication spawned MeGI’s regulator OGI, completing the path leading to dioecy. These findings exemplify how duplication events can provide flexible genetic material available to help respond to varying environments and provide interesting parallels for our understanding of the mechanisms underlying the transition into dieocy in plants.

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April 21, 2020

Convergent evolution of linked mating-type loci in basidiomycetes: an ancient fusion event that has stood the test of time

Sexual development is a key evolutionary innovation of eukaryotes. In many species, mating involves interaction between compatible mating partners that can undergo cell and nuclear fusion and subsequent steps of development including meiosis. Mating compatibility in fungi is governed by mating type determinants, which are localized at mating type (MAT) loci. In basidiomycetes, the ancestral state is hypothesized to be tetrapolar (bifactorial), with two genetically unlinked MAT loci containing homeodomain transcription factor genes (HD locus) and pheromone and pheromone receptor genes (P/R locus), respectively. Alleles at both loci must differ between mating partners for completion of sexual development. However, there are also basidiomycete species with bipolar (unifactorial) mating systems, which can arise through genomic linkage of the HD and P/R loci. In the order Tremellales, which is comprised of mostly yeast-like species, bipolarity is found only in the human pathogenic Cryptococcus species. Here, we describe the analysis of MAT loci from the Trichosporonales, a sister order to the Tremellales. We analyzed genome sequences from 29 strains that belong to 24 species, including two new genome sequences generated in this study. Interestingly, in all of the species analyzed, the MAT loci are fused and a single HD gene is present in each mating type. This is similar to the organization in the pathogenic Cryptococci, which also have linked MAT loci and carry only one HD gene per MAT locus instead of the usual two HD genes found in the vast majority of basidiomycetes. However, the HD and P/R allele combinations in the Trichosporonales are different from those in the pathogenic Cryptococcus species. The differences in allele combinations compared to the bipolar Cryptococci as well as the existence of tetrapolar Tremellales sister species suggest that fusion of the HD and P/R loci and differential loss of one of the two HD genes per MAT allele occurred independently in the Trichosporonales and pathogenic Cryptococci. This finding supports the hypothesis of convergent evolution at the molecular level towards fused mating-type regions in fungi, similar to previous findings in other fungal groups. Unlike the fused MAT loci in several other basidiomycete lineages though, the gene content and gene order within the fused MAT loci are highly conserved in the Trichosporonales, and there is no apparent suppression of recombination extending from the MAT loci to adjacent chromosomal regions, suggesting different mechanisms for the evolution of physically linked MAT loci in these groups.

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April 21, 2020

Complete genome sequence and evolution analysis of Psychrobacter sp. YP14 from Gammaridea Gastrointestinal Microbiota of Yap Trench

Psychrobacter sp. YP14, a moderately psychrophilic bacterium belonging to the class Gammaproteobacteria, was isolated from Gammaridea Gastrointestinal Microbiota of Yap Trench. The strain has one circular chromosome of 2,895,311 bp with a 44.66% GC content, consisting of 2333 protein-coding genes, 53 tRNA genes and 9 rRNA genes. Four plasmids were completely assembled and their sizes were 13,712 bp, 19711 bp, 36270 bp, 8194 bp, respectively. In particular, a putative open reading frame (ORF) for dienelactone hydrolase (DLH) related to degradation of chlorinated aromatic hydrocarbons. To get an better understanding of the evolution of Psychrobacter sp. YP14 in this genus, six Psychrobacter strains (G, PRwf-1, DAB_AL43B, AntiMn-1,P11G5, P2G3), with publicly available complete genome, were selected and comparative genomics analysis were performed among them. The closest phylogenetic relationship was identified between strains G and K5 based on 16s gene and ANI (average nucleotide identity) values. Analysis of the pan-genome structure found that YP14 has fewer COG clusters associated with transposons and prophage which indicates fewer sequence rearrangements compared with PRwf-1. Besides, stress response-related genes of strain YP14 demonstrates that it has less strategies to cope with extreme environment, which is consistent with its intestinal habitat. The difference of metabolism and strategies coped with stress response of YP14 are more conducive to the study of microbial survival and metabolic mechanisms in deep sea environment.

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April 21, 2020

The Chinese chestnut genome: a reference for species restoration

Forest tree species are increasingly subject to severe mortalities from exotic pests, diseases, and invasive organisms, accelerated by climate change. Forest health issues are threatening multiple species and ecosystem sustainability globally. While sources of resistance may be available in related species, or among surviving trees, introgression of resistance genes into threatened tree species in reasonable time frames requires genome-wide breeding tools. Asian species of chestnut (Castanea spp.) are being employed as donors of disease resistance genes to restore native chestnut species in North America and Europe. To aid in the restoration of threatened chestnut species, we present the assembly of a reference genome with chromosome-scale sequences for Chinese chestnut (C. mollissima), the disease-resistance donor for American chestnut restoration. We also demonstrate the value of the genome as a platform for research and species restoration, including new insights into the evolution of blight resistance in Asian chestnut species, the locations in the genome of ecologically important signatures of selection differentiating American chestnut from Chinese chestnut, the identification of candidate genes for disease resistance, and preliminary comparisons of genome organization with related species.

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April 21, 2020

Benchmarking Transposable Element Annotation Methods for Creation of a Streamlined, Comprehensive Pipeline

Sequencing technology and assembly algorithms have matured to the point that high-quality de novo assembly is possible for large, repetitive genomes. Current assemblies traverse transposable elements (TEs) and allow for annotation of TEs. There are numerous methods for each class of elements with unknown relative performance metrics. We benchmarked existing programs based on a curated library of rice TEs. Using the most robust programs, we created a comprehensive pipeline called Extensive de-novo TE Annotator (EDTA) that produces a condensed TE library for annotations of structurally intact and fragmented elements. EDTA is open-source and freely available: https://github.com/oushujun/EDTA.List of abbreviationsTETransposable ElementsLTRLong Terminal RepeatLINELong Interspersed Nuclear ElementSINEShort Interspersed Nuclear ElementMITEMiniature Inverted Transposable ElementTIRTerminal Inverted RepeatTSDTarget Site DuplicationTPTrue PositivesFPFalse PositivesTNTrue NegativeFNFalse NegativesGRFGeneric Repeat FinderEDTAExtensive de-novo TE Annotator

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April 21, 2020

Insights into the bacterial species and communities of a full-scale anaerobic/anoxic/oxic wastewater treatment plant by using third-generation sequencing.

For the first time, full-length 16S rRNA sequencing method was applied to disclose the bacterial species and communities of a full-scale wastewater treatment plant using an anaerobic/anoxic/oxic (A/A/O) process in Wuhan, China. The compositions of the bacteria at phylum and class levels in the activated sludge were similar to which revealed by Illumina Miseq sequencing. At genus and species levels, third-generation sequencing showed great merits and accuracy. Typical functional taxa classified to ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), denitrifying bacteria (DB), anaerobic ammonium oxidation bacteria (ANAMMOXB) and polyphosphate-accumulating organisms (PAOs) were presented, which were Nitrosomonas (1.11%), Nitrospira (3.56%), Pseudomonas (3.88%), Planctomycetes (13.80%), Comamonadaceae (1.83%), respectively. Pseudomonas (3.88%) and Nitrospira (3.56%) were the most predominating two genera, mainly containing Pseudomonas extremaustralis (1.69%), Nitrospira defluvii (3.13%), respectively. Bacteria regarding to nitrogen and phosphorus removal at species level were put forward. The predicted functions proved that the A/A/O process was efficient regarding nitrogen and organics removal. Copyright © 2019 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

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April 21, 2020

Next-Generation Sequencing and Emerging Technologies.

Genetic sequencing technologies are evolving at a rapid pace with major implications for research and clinical practice. In this review, the authors provide an updated overview of next-generation sequencing (NGS) and emerging methodologies. NGS has tremendously improved sequencing output while being more time and cost-efficient in comparison to Sanger sequencing. The authors describe short-read sequencing approaches, such as sequencing by synthesis, ion semiconductor sequencing, and nanoball sequencing. Third-generation long-read sequencing now promises to overcome many of the limitations of short-read sequencing, such as the ability to reliably resolve repeat sequences and large genomic rearrangements. By combining complementary methods with massively parallel DNA sequencing, a greater insight into the biological context of disease mechanisms is now possible. Emerging methodologies, such as advances in nanopore technology, in situ nucleic acid sequencing, and microscopy-based sequencing, will continue the rapid evolution of this area. These new technologies hold many potential applications for hematological disorders, with the promise of precision and personalized medical care in the future.Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

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April 21, 2020

Draft genome sequence resource of switchgrass rust pathogen, Puccinia novopanici isolate Ard-01.

Puccinia novopanici is an important biotrophic fungal pathogen that causes rust disease in switchgrass. Lack of genomic resources for P. novopanici has hampered the progress towards developing effective disease resistance against this pathogen. Therefore, we have sequenced the whole genome of P. novopanici and generated a framework to understand pathogenicity mechanisms, identify effectors, repeat element invasion, genome evolution, and comparative genomics among Puccinia species in the future. Long and short read sequences were generated from P. novopanici genomic DNA by PacBio and Illumina technologies, respectively, and assembled a 99.9 megabase (Mb) genome. Transcripts of P. novopanici were predicted from assembled genome using MAKER and were further validated by RNAseq data. The genome sequence information of P. novopanici will be a valuable resource for researchers working on monocot rusts and plant disease resistance in general.

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April 21, 2020

Genome Sequence Resource of a Puccinia striiformis Isolate infecting wheatgrass.

Stripe rust caused by Puccinia striiformis is a disastrous disease of cereal crops and various grasses. To date, fourteen stripe rust genomes are publicly available, including thirteen P. striiformis f. sp. tritici and one P. striiformis f. sp. hordei. In this study, one isolate (11-281) of P. striiformis collected from wheatgrass (Agropyron cristatum), which is avirulent to most of standard differential genotypes of wheat and barley, was sequenced, assembled, and annotated. The sequences were assembled to a draft genome of 84.75 Mb, which is comparable to previously sequenced P. striiformis f. sp. tritici and P. striiformis f. sp. hordei isolates. The draft genome comprised 381 scaffolds and contained 1,829 predicted secreted proteins. The high quality draft genome of the isolate is a valuable resource in shedding light on the evolution and pathogenicity of P. striiformis.

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April 21, 2020

Genome analysis and Hi-C assisted assembly of Elaeagnus angustifolia L., a deciduous tree belonging to Elaeagnaceae

Elaeagnus angustifolia L. is a deciduous tree of the Elaeagnaceae family. It is widely used in the study of abiotic stress tolerance in plants and for the improvement of desertification-affected land due to its characteristics of drought resistance, salt tolerance, cold resistance, wind resistance, and other environmental adaptation. Here, we report the complete genome sequencing using the Pacific Biosciences (PacBio) platform and Hi-C assisted assembly of E. angustifolia. A total of 44.27 Gb raw PacBio sequel reads were obtained after filtering out low-quality data, with an average length of 8.64 Kb. Assembly using Canu gave an assembly length of 781.09 Mb, with a contig N50 of 486.92 Kb. A total of 39.56 Gb of clean reads was obtained, with a sequencing coverage of 75×, and Q30 ratio > 95.46%. The 510.71 Mb genomic sequence was mapped to the chromosome, accounting for 96.94% of the total length of the sequence, and the corresponding number of sequences was 269, accounting for 45.83% of the total number of sequences. The genome sequence study of E. angustifolia can be a valuable source for the comparative genome analysis of the Elaeagnaceae family members, and can help to understand the evolutionary response mechanisms of the Elaeagnaceae to drought, salt, cold and wind resistance, and thereby provide effective theoretical support for the improvement of desertification-affected land.

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